<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>aside</title>
    <!-- aside标签是侧边栏标签，定义侧边栏、广告、nav元素组 -->
    <link rel="stylesheet" href="index.css" />
</head>
<body>
<section>
    <aside class="left">
        <ul>
            <li>left-nav1</li>
            <li>left-nav2</li>
            <li>left-nav3</li>
            <li>left-nav4</li>
        </ul>
    </aside>
    <aside class="right">
        <ul>
            <li>right-nav1</li>
            <li>right-nav2</li>
            <li>right-nav3</li>
            <li>right-nav4</li>
        </ul>
    </aside>
</section>
</body>
</html>